Communication systems of various kinds are known in the art. Many such systems support the conveyance of speech. In its natural or fully digitized form speech can consume a considerable amount of bandwidth. A strong needs exists, however, to limit bandwidth usage in many communication systems to thereby permit supporting a large user base. Vocoding techniques are often employed to meet these concurrent but sometimes opposing needs.
Various forms of vocoding are known. In general, digitized speech is analyzed and then characterized by representative parameters. These parameters are usable to effect reconstruction of the original speech content and typically require considerably less bandwidth to effect their conveyance.
It is also known that vocoding information can be damaged during transit. Wireless communication systems are particularly susceptible to such phenomena. Because speech transmissions are often real time sessions there will usually not be sufficient time to permit a damaged parcel of vocoding information to be replaced. Accordingly, many modern vocoding systems will recognize when a given frame of vocoded voice has been damaged or otherwise sufficiently corrupted during transit (to a point where the vocoder information cannot be reliably decoded) and can categorize such a frame as being “erased.” Upon recognizing that a given vocoded voice frame is erased, any of a variety of techniques (such as interpolation, insertion of noise, and so forth) can be employed to at least attempt to minimize the impact of the lost information.
Unfortunately, not all systems can reliably ascertain the existence of an erased frame of vocoder information. More particularly, not all mobile stations may be configured to reliably detect when a given received vocoder frame is, in fact, erased. Problems such as this can arise, for example, as system protocols advance with time and legacy user equipment fails to remain completely current with all operating protocols.
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